Application of acute maximal exercise to protect orthostatic
tolerance following 16 days of simulated microgravity.
Engelke, Keith A., Donald F. Doerr, Craig G. Crandall and Victor A. Convertino.
Department of Physiology, University of Florida, Gainesville, FL
32610; NASA-Kennedy Space Center, FL 32899; Physiology Research
Branch, Clinical Science Division, Brooks Air Force Base, TX
78235
APStracts 3:0124R, 1996.
We tested the hypothesis that one bout of maximal exercise performed
at the conclusion of prolonged simulated microgravity would improve
blood pressure stability during an orthostatic challenge. Heart rate
(HR), mean arterial blood pressure (MAP), norepinephrine (NE),
epinephrine (EPI), arginine vasopressin (AVP), plasma renin activity
(PRA), atrial natriuretic peptide (ANP), cardiac output (O(Q, x )),
forearm vascular resistance (FVR), and changes in leg volume were
measured during lower body negative pressure (LBNP) to presyncope in
7 subjects immediately prior to re-ambulation from 16 days of 6 head
-down tilt (HDT) under two experimental conditions: 1) after maximal
supine cycle ergometry performed 24 h prior to returning to the
upright posture (exercise) and 2) without exercise (control). After
HDT, the reduction of LBNP tolerance time from pre-HDT levels was
greater (P = 0.041) in the control condition (-2.0 +/- 0.2 min)
compared to the exercise condition (-0.4 +/- 0.2 min). At presyncope
after HDT, FVR and NE were higher (P < 0.05) following exercise
compared to control while MAP, HR, EPI, AVP, PRA, ANP, and leg volume
were similar in both conditions. Plasma volume (PV) and carotid
-cardiac baroreflex sensitivity were reduced after control HDT, but
were restored by the exercise treatment. Maintenance of orthostatic
tolerance by application of acute intense exercise after 16 days of
simulated microgravity was associated with greater circulating levels
of NE, vasoconstriction, O(Q, x ), and baroreflex sensitivity, and
PV.
Received 6 June 1995; accepted in final form 1 March 1996.
APS Manuscript Number R333-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96